1. Technical Field
Embodiments of the present invention relate to digital image processing. More specifically, embodiments of the invention relate to methods for joint automatic demosaicking and white balancing of a color filter array (CFA) single-sensor image.
2. Related Art
A digital image is a representation of a two-dimensional analog image as a finite set of pixels. Digital images can be created by a variety of devices, such as digital cameras, scanners, and various other computing devices. Digital image processing is the use of computer algorithms to perform image processing on digital images. Image processing operations include, for example, demosaicking, white balancing, color to grayscale conversion, color adjustment, intensity adjustment, scene analysis, and object recognition. Demosaicking refers to the process of interpolating a full-color digital image from mosaic data received from a CFA internal to many digital cameras. White balancing refers to the process of adjusting the color in a digital image in order to compensate for color shifts due to scene illumination.
In common single-sensor digital camera imaging pipelines, automatic white-balancing solutions are used before or after the demosaicking step to adjust the coloration of the captured visual data in order to compensate for the scene illuminant. Since demosaicking restores the full-color information from the gray-scale CFA sensor readings, the white balancing after demosaicking approach is significantly slower than the white balancing before demosaicking approach when using the same white-balancing solution. On the other hand, white-balancing solutions usually adjust chrominance components (i.e., R and B components of color images in a common Red-Green-Blue format) using luminance components (i.e., G components of color images in a common Red-Green-Blue format). Since in CFA images the pixel locations with available chrominance samples lack the luminance component, which thus has to be estimated prior to adjusting the chrominance component, the white balancing before demosaicking approach may not be as accurate as the white balancing after demosaicking approach when using the same powerful demosaicking solution.